A core bit that is retractable through a drill string and tools for replacing the bit on the drill stem.
During drilling operations, for example exploring for minerals, the drill bit wears and has to be replaced in order to carry out an efficient operation. Withdrawing the drill string to remove, inspect and/or replace the drill bit is a time consuming task and leaves the drill hole subject to caving by unstable formations along the hole path. Drill bits have been made in the past that are replaceable on the drill string without withdrawing the drill string, but such past attempts have not been commercially successful.
Two general categories of prior art systems have been evolved to eliminate having to pull the entire drill string to replace a worn or damaged bit as follows: (1) collapsible bits and (2) pilot bit with retractable reamer. Collapsible bits are made of many segments which may travel through the drill string as a group and unfold or spread out upon reaching the axial inner end of the drill string, for example see U.S. Pat. No. 3,603,413; or in line one above the other through the drill string and guided into position at the axial inner end of the drill string where they are locked in place for drilling, for example see U.S. Pat. No. 3,437,159. Such segmented bits must be machined into intricate shapes, which is costly, and the drill operator is not always sure the bit segments are locked in place for drilling. Further, grit from the drilling operation can interfere with the proper exchange of bits.
An example of a pilot bit with an expandable reamer are U.S. Pat. Nos. 3,894,590 and 474,080. This type of system is subject to problems such as mentioned with reference to collapsible bit systems.
U.S. Pat. No. 3,965,996 discloses a bit assembly that is lowered through a drill string with its drill axis transverse to the longitudinal axis of the drill string and when locked in a drilling position has its drill axis generally aligned with the drill string axis. However, such a bit is not suitable for taking a core sample.
U.S. Pat. No. 3,545,553 discloses coupling apparatus for mounting and moving bits through a drill string, the coupling apparatus being hydraulically operated to latchingly engage the drill string. The coupling apparatus includes cam mechanism to angularly align its coupling members with drill string slots. The coupling apparatus remains latched to the drill stem while the hole is being drilled.
In order to provide a commercially feasible retractable bit system for replacing a drill bit without removing the drill string from the drill hole, and that can be used for core drilling, this invention has been made.